Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper, transparency film, or textiles. Essentially, ink-jet printing involves the ejection of fine droplets of ink onto print media in response to electrical signals generated by a microprocessor.
There are two basic means currently available for achieving ink droplet ejection in ink-jet printing: thermally and piezoelectrically. In thermal ink-jet printing, the energy for drop ejection is generated by electrically-heated resistor elements, which heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble, resulting in the expulsion of ink through nozzles associated with the resistor elements. In piezoelectric ink-jet printing, the ink droplets are ejected due to the vibrations of piezoelectric crystals, again, in response to electrical signals generated by the microprocessor. The ejection of ink droplets in a particular order forms alphanumeric characters, area fills, and other patterns on the print medium.
Ink-jet printers offer low cost, high quality printing with relatively noise-free operation. As such, ink-jet printers have become a popular alternative to other types of printers. However, ink-jet printers are presently incapable of matching the level of throughput generated by laser printers due in large part to the relatively slow dry time of ink-jet inks as well as to the printer slow-down deriving from the resident bleed control algorithm in the printer. With particular regard to bleed control, there is a tendency among ink-jet inks to bleed into one another when printed in various colors on paper substrates. Bleed occurs as colors mix both on the surface of the paper substrate as well as within the substrate itself. In response to this problem, ink-jet printers commonly employ bleed control algorithms in an attempt to provide a border between colors that is clean and free from the invasion of one color into another; however, this slows down the printer. In order to increase the level of throughput generated by ink-jet printers, the dry time of ink-jet inks should be improved, preferably in a manner that also affects bleed control.
Various solutions to the problem of black to color and color to color bleed have been proffered. Some solutions involve changing the ink environment to reduce bleed. For instance, heated platens and other heat sources, along with specially formulated paper, have been employed to reduce bleed. However, heated platens add cost to the printer, and specially formulated paper is more expensive than "plain" paper. Thus, using external paraphernalia to reduce bleed in ink-jet color printing is generally not cost effective. Another commonly employed method for reducing bleed involves the use of bleed control algorithms in ink-jet printers to provide borders between colors that are clean and free from the invasion of one color into another; however, such algorithms slow down the printer.
Other proposed solutions to the problem of bleed involve changing the composition of an ink-jet ink. For example, surfactants have been effectively used to reduce bleed in dye-based ink formulations; see, e.g., U.S. Pat. No. 5,106,416 entitled "Bleed Alleviation Using Zwitterionic Surfactants and Cationic Dyes," issued to John Moffatt et al., U.S. Pat. No. 5,116,409 entitled "Bleed Alleviation in Ink-Jet Inks", issued to John Moffatt, and U.S. Pat. No. 5,133,803 entitled "High Molecular Weight Colloids Which Control Bleed", issued to John Moffatt, all assigned to the same assignee as the present application. However, surfactants increase the penetration rate of the ink into the paper, which may also result in the reduction of edge acuity. Moreover, the addition of surfactant-containing inks could cause puddles on the nozzle plates of the printhead, leading to poor drop ejection characteristics. Other solutions specific to dye-based ink compositions, disclosed in patents assigned to the present assignee, are found in U.S. Pat. No. 5,198,023, entitled "Cationic Dyes with Added Multi-Valent Cations to Reduce Bleed in Thermal Ink-Jet Inks", issued to John Stoffel, and U.S. Pat. No. 5,181,045, entitled "Bleed Alleviation Using pH Sensitive Dyes, issued to James Shields et al., both assigned to the same assignee as the present application.
U.S. Pat. No. 5,565,022, entitled "Fast Drying, Bleed-Free Ink-Jet Ink Compositions," assigned to the same assignee as the present application, and incorporated herein by reference, is directed to bleed control of dye-based ink compositions wherein the dye is either water-soluble or water-insoluble (i.e., solvent-soluble dye). More specifically, bleed control for such inks is achieved by dissolving the dye in either water or the solvent depending on the nature of the dye. The ink is in the form of a microemulsion which is an isotropic solution of water, a water-insoluble organic compound, and an amphiphile, there being sufficient amphiphile to solubilize the water-insoluble compound in water.
U.S. Pat. No. 5,531,816, entitled "Bleed-Alleviated, Waterfast, Pigment-Based Ink-Jet Ink Compositions," and U.S. Pat. No. 5,713,989, entitled "Bleed Alleviated Aqueous Pigment Dispersion-Based Ink-Jet Ink Compositions," both assigned to the same assignee as the present application, and incorporated herein by reference, are directed to bleed control of solvent-dispersed pigment-based, and aqueous pigment-based ink-jet ink compositions, respectively. More specifically, bleed control for such inks is achieved by dispersing the pigment and keeping it in solution in the form of a microemulsion. Again, however, these solutions to bleed are not directed to dye-based inks, but rather are specifically directed to dispersed pigment-based inks.
Furthermore, the suitable ink-jet ink has to provide for other performance attributes as well. In order to obtain a robust print sample, the ink should be capable of producing lightfast images once printed on the print medium. Typically, lightfastness has been achieved for black ink by using pigment-based inks. However, the color inks; e.g., magenta, yellow, and cyan; typically use dye as the coloring agent, thus leading to less lightfast images. Another problem, has been the selective bleed control--even though bleed control has been achieved between some of the colors, it has not been achieved between all possible combinations between the four major colors of black, magenta, yellow, and cyan.
Accordingly, a need exists for ink-jet printing systems that can provide improved print quality, specifically, reduced bleed; improved edge-acuity, uniform area fills, and color quality; while maximizing lightfastness without sacrificing printing reliability.